The systems in our bodies are intricately interconnected. However, this biological fact was not always evident to doctors and scientists.

From physical impacts to chemical messages, scientific research has gradually uncovered the complex and varied ways muscle and bone communicate with each other and the rest of the body.

This article will review how the muscular system and the skeletal system are interlinked, how they interact with each other, and how we can use our enhanced understanding to improve bone health.

Bone And Muscle Are Strong Together Or Weak Together

Bones and muscles depend on each other to remain strong and healthy. A clear indication of this codependency is the coincidence of osteoporosis and sarcopenia.

Sarcopenia describes a significant loss of muscle mass. Less muscle reduces strength and increases the risk of falls and injuries. Those falls are more dangerous with the bone loss that characterizes osteoporosis.

Studies have found that both muscle and bone deteriorate jointly in the face of factors like disuse, disease, and the process of aging.¹

The age-related degeneration of muscle and bone can start a vicious cycle of heightened risk as the loss can cause reduced mobility, which furthers the cycle of loss and increases the risks of falls and fractures.

For many decades, a biomechanical explanation was the sole model for how muscle and bone interact. Wolff's Law describes how bone adapts to use in response to the strain muscles place on them. Scientists observed this process and concluded that this mechanical interaction governed the relationship between the two tissues.

However, experiments with mice suggested that there might be another essential part of the communication between muscle and bone.¹

Studies that manipulated molecular signaling compounds found that when certain chemicals were blocked or artificially overproduced, the relationship between bone mass and muscle mass changed in unexpected ways. Bone and muscle stopped following the growth and loss pattern that a purely physical cause-and-effect relationship would dictate.¹

Researchers theorized that muscle and bone must communicate additionally by producing and receiving chemical compounds.¹

Synopsis

Bone and muscle grow and deteriorate together. The co-incidence of osteoporosis and sarcopenia demonstrates this relationship. The connection between the two tissues has long been thought to be purely physical, but recent evidence has shown that the tissues also directly communicate using chemical messengers.

How Bone And Muscle Speak To Each Other

In addition to their best-known functions, the skeletal and muscular systems are also secretory endocrine organs. Bones and muscles are able to secrete hormones that trigger responses elsewhere in the body.

Researchers found that after exercise, muscles secrete chemical factors into circulation that affect other tissues.¹ These factors are called myokines, which are small proteins and peptides that signal the release of hormones.

Interleukin 6 (IL-6) was among the first myokines identified. Muscles produce significant amounts of IL-6 during exercise. Many other myokines have been discovered since, with different effects on other systems in the body, including bone.¹

More recently, scientists discovered that bone is also an endocrine organ. For many years researchers observed that bone was the target of endocrine messaging. The tissue responds to hormones like parathyroid hormone (PTH) and sex hormones.¹

However, an increasing amount of data demonstrates that bone produces chemical factors that instruct other tissues. These factors are called osteokines, and they affect tissues comprising muscle, the liver, the kidneys, and the pancreas.¹

One of those factors is osteocalcin, which is secreted mainly by osteoblasts, the cells responsible for depositing new bone.

Sclerostin, a compound recently targeted by osteoporosis drug-makers, is an osteokine secreted mainly by osteocytes, the cells responsible for resorbing old and damaged bone.

Scientists have observed how these myokines and osteokines serve to communicate between muscle and bone. Mice with elevated circulating levels of IL-15, produced by muscle, were found to have increased bone mineral content. Another interleukin myokine was found to promote osteoclastogenesis (the formation of osteoclasts, which are the cells that break down bone).¹

Researchers found that delivery of osteocalcin to muscle prior to exercise increased the exercise capacity of young mice and restored aerobic endurance in old mice. Osteocalcin even increased muscle mass in old mice.¹

Synopsis

Researchers have discovered that muscle and bone are both endocrine organs, capable of secreting chemical factors that send instructions to each other and to other tissues in the body. Studies have observed factors like interleukin 6 (IL-6), osteocalcin, and sclerostin used as chemical signals for communication between bone and muscle.

Other Links Point To Other Pathways

The physical relationship between bone and muscle and the chemical messages they each produce are not the only links that connect these two systems.

Researchers note that some genetic determinants of each system may be shared between them. Individual genes often impact multiple body systems, and this is likely the case with muscle and bone.¹

Furthermore, environment and behavior can influence gene expression, which means those factors may impact bone and muscle together.

Connective tissues, including tendons, ligaments, cartilage, and others, may be facilitating forms of cross-talk that haven't yet been identified.

The nervous system is another likely communication pathway. It plays a role in regulating bone mass and also governs muscle contraction as well as playing a role in muscle development.

Synopsis

Muscles and bones may be using other systems and pathways to communicate. Researchers point to shared genetic determinants, connective tissues, and the nervous system as potential conduits of communication.

The Practical Side Of This Knowledge

The interconnectedness of muscles and bones means that a problem with either system is best addressed through both systems. It also means that using drugs to block or mimic one particular chemical signal will always have side effects that are unintended and undesirable.

The endless list of side effects of osteoporosis drugs demonstrates the imprecision and risk of attempting to chemically alter the bone formation process.

Instead of relying on ineffective and risky drugs that overlook the complexity of our bodies, we can use our interconnected body systems to strengthen and repair them together.

The simplest example of an all-natural dual-system intervention is exercise. Through exercise you use and strengthen muscles, and those muscles use the communication systems you learned about today to trigger the growth of new, stronger bones.

You can activate this positive feedback system right now by lacing up your shoes and taking a brisk walk on your favorite trail or sidewalk. Build a set of physical activity habits that fit into your day, reflect your interests, and engage your body. For example, you could set a pattern of working out with an exercise video a few times a week, joining a weekly aerobics class, and going on a daily walk.

Synopsis

We know that bone and muscle communicate with each other in response to how we use them. Build patterns of regular physical activity to spur your muscles and bones to collaborate on building strength and physical ability.

What This Means To You

Your body is incredible and complex, and fortunately, we know more about how it works now than ever before in human history.

The Osteoporosis Reversal Program was developed to apply that knowledge to improve your bone health and overall health. It offers an in-depth look at bone loss, the mechanics of building bone, and the many body systems we can support to prevent and reverse osteoporosis.

Use the knowledge that centuries of scientific study have accumulated to take safe and effective action to improve your bone health and live the life you deserve.

References

¹ https://www.mdpi.com/2227-9059/5/4/62